Plant development L1- Origin of flowering plants

Origin of flowering plants

The plants that coexisted with dinosaurs were very different: Conifers, ferns

No flowering plants at all

This includes grasses which our civilisation now highly relies on

1 of 15

What is Darwin's abominable mystery?

A long time ago there were no flowers and then suddenly the world was covered in flowering plants.

The mystery is that 150-200 mya, something happened and there is no fossil record indicating where flowering plants came from.

The mystery?

- Where did flowering plants come from and how did they take over the globe so rapidly.
- In the Dinosaur period, gymnosperms were all that existed and now only a few hundred gynosperms left as they have almost completely been displaced by angiosperms
- There are about 400,000 angiosperms that occupy a vast range of niches
- They have done this by inventing new evolutionary innovations.

2 of 15

Angiosperms

Amborella is the sister plant of all other flowering plants on earth and it appears to be the oldest branching plant on earth.

The next one up, Nymphaeceae, includes the waterlilies.

There is a paper that argues that in fact the waterlilies are the oldest plant.

Molecular evidence suggests that it is Amborella that is the sister to all other branching plants.

Some developmental evidence suggesting otherwise.

Also includes the monocots: These contain the grasses that support most human life. Rice, wheat and maize in particular.

As you move closer the present day, the development of the flower become more defined.

3 of 15

Brassicales

Includes the Arabidopsis thaliana- The world's favourite model plant

4 of 15

R.arnoldii

The world’s biggest flower

1m across

10kg

Stinking corpse lily- It very efficiently manipulates the behaviour of animals to do things that it cannot. The plant is stuck where it is living and cannot move around so it needs to coerce animals.

Looks like rotting meat and smells like it so it attracts carrying fly which pick up pollen and transfer it to another flower that smells the same.

It is entirely parasitic plant, it does not have any leaves and lives entirely off plants that it parasitizes around it

5 of 15

W. australiana

The W. australiana is the world’s smallest flower and is about 250,000 times smaller than the R. arnoldii

It is a little aquatic flower that has male and female organs, reproduces, sets seeds. Do not have the smallest seeds.

This is just to illustrate the diversity that flowering plants have

6 of 15

Flowering plants manipulate animal behaviour

Flowering plants are largely pollinated by insects and birds

They can also be pollinated by nocturnal animals such as bats

Also, larger animals that eat the fruits of the plant and deposit the seeds of the fruit away from the mother plants in their waste

7 of 15

Western Underground Orchid

It lives entire life underground, including flowering

Only lives in Australia

Only discovered when farmer was ploughing a field and found that he had dug up a load of the orchids that were flowering

Pollinated by underground insects

It is now endangered,and it is believed that this is because it is thought to have relied on a marsupial that is not extinct for its dispersal

This just illustrates that these plants have come to occupy very diverse niches

Also, because it is entirely underground it cannot PS

It is another parasitic plant, but does not even make contact with host plant, it derives its nutrition from a fungus that links it to host plant.

8 of 15

Arabidopsis

Lots of different species- thaliana is just one of them

They are durable

Easy to work with

This was the first plant to have its genome sequences- In 2000

Genome is well annotated now

Arabidopsis is great for genetics- it is a diploid plant with a fairly reduced genome, fairly easy to make crosses

There are stock centres around the world where material is provided to research the species

It can be transformed very easily and make transgenic Arabidopsis lines

This allows you to do reverse genetics- Have a gene that you feel might be important and finding out what it does.

Looking at what a gene does you then study mutant in whih gene has been knoched out and look at how this effects the phenotype of the plant.

9 of 15

Why use Arabidopsis?

Speed- Can get 8 generations in a year, which is very fast

Size- A very small plant, which means that there is a lot less resources needed to grow and examine this plant compared to maize that would require and extremely large area of field with an army of people- CHEAPER

All of these reasons combined has led to a much larger community of Arabidopsis thaliana than other communities.

This allows momentum and allows you to gain progress much quicker than in other species

Self's- A lot of plants, especially those that are of interest to sciene, are self-incopatible but A. thaliana is very easy to self.

It does it on its own, and if you don't want it to self you have to prevent this.

10 of 15

Alternation of generations

Plants have 2 parts to their lifecycle:

A diploid sporophyte stage

A haploid gametophyte stage

The major part of most plant lifecycles is the diploid sporophyte part but there are some plants in which the gametophyte is the dominant phase (Moss etc)

The diploid phase ends with meiosis to make haploid male and female gametes

The diploid phase starts following the fertilisation of the female haploid gamete by the male hg.

11 of 15

Haploid phase

Meiosis is the start of the haploid stage

Meiosis is obviously different in the male and female gametophytes

Males- Gametophyte is formed in the stamen

Female- Gametophute formed in the carpel

Male; Stamen is made up of a filament and anther

Anther: Where the pollen grains form

Inside it there are pollen sacs which contains diploid cells called microspore mother cells

In the transition to the gametophyte stage the microspore mother cell undergoes meiosis to produce 4 microspores

Each one of these undergoes mitosis to produce a pollen grain which contains 2 haploid cell

12 of 15

What about in female organs?

Gametophyte is formed within the ovule which is within the carpel

There are lots of ovules in a carpel

A single cell ( the megaspore mother cell that is diploid) undergoes meiosis to produce 4 haploid megaspores

3 of these megaspores die leaving one surviving megaspore

The surviving megaspore then goes through 3 rounds of mitosis to produce 8 nuclei without cellularisation (effectively have one big cell with 8 nuclei)

These 8 nuclei then get partitioned into 7 cells with one cell containing 2 nuclei (diploid)

3 at one end that are called the antipodal cells

No understanding of what these do

There is then a cell in the middle

This is the endosperm cell which contains 2 nuclei

There are also 3 cells at the other end of the embryo sac.

The 2 on the outside are called synergids and the central cell is the egg cell

The egg cell will be fertilised to produce zygote

13 of 15

Diploid phase

You have the embryo which is within a seed

This undergoes germination

In this is goes through primary development which is sometimes known as vegetative development

Then you will go through secondary development which is known as reproductive development in which it will flower (angiosperms)

Sometimes the vegetative phase is split into juvenile and adult phase

14 of 15

Secondary fertilisation

The pollen grain lands on the top of the carpel on the stigmatic papillae

The pollen grain then germinates and produces a pollen tube which grows down transmitting tissues to the bottom of the ovule through the micropyle and releases the 2 nuclei

One of them fertilises the egg cell which will become the diploid zygote and the other one fertilises the diploid endosperm cell to make a triploid tissue (endosperm) whcih provides nutrition for the developing embryo